THE ARGENTINE ANT IN RELATION TO CITRUS GROVES. 

 Experiment VI. 



31 



In the following experiment, verifying the results of the one pre- 

 ceding, 4 trees longer subject to unchecked black-scale infestation 

 were used, 2 of them being banded on June 2, the other 2 left free 

 to ants. 



Table VII. — Effect of Argentine ant on abundance o fmealybugs in the presence 

 of heavy black-scale infestation on orange. Los Angeles County, Cal., 1916. 





Acts present. 



Ants excluded. 



Date. 



Fru"t infestation. 



Fruit infestation. 





With 

 mealy- 

 bugs. 



With 

 black 

 scale. 



With 

 sooty 

 mold. 



With 



mealy- 

 bugs. 



With 

 black 

 scale. 



With 

 sooty 

 mold. 





Per cent. 

 37.5 

 32.9 

 48.1 

 39.6 



Per cent. 



Per cent. 



Per cent. 

 32.5 



Per cent. 



Per cent. 





94.4 

 53.5 



91.7 



100 



100 

 100 



20.2 

 20.5 

 21.2 



100 

 45.7 

 98.7 



100 





100 



Sept 11 



100 







The fruit infestation on different dates, summarized in Table VII, 

 shows that mealybugs were always somewhat more numerous on the 

 fruit patrolled by ants, but that almost no change in degree of in- 

 festation occurred on either lot of trees. Most of the fruit on all 

 trees was infested with young black scales, and all was sooty through- 

 out the experiment. 



EELATION OF THE ANT TO MEALYBUG OUTBREAKS IN SOUTHERN CALIFORNIA. 



The foregoing experiments establish beyond a doubt that the at- 

 tendance of ants upon mealybugs in Los Angeles County, Cal., has 

 the effect of greatly increasing their abundance, particularly during 

 the first half of the summer, upon healthy trees comparatively free 

 from other scale insects, causing severe infestations where otherwise 

 they would be so scarce as hardly to come to notice at all. 



This does not mean, however, that the mealybug outbreaks do not 

 occur in southern California except in the presence of ants. More 

 than 300 outbreaks of the citrus and other species of mealybugs were 

 reported during the summer of 1916 in and about Pasadena by Dr. 

 A. G. Smith, the local county inspector. The writer inspected 167 of 

 these for ants, but, while the Argentine ant was present in 72 of 

 them, and other ants in 16 more, there were no ants in the remaining 

 79. Nevertheless, it is a fact that in Los Angeles County the enemies 

 of the citrus mealybug bring it under control early in the season and 

 generally cause its almost complete disappearance when there are no 

 ants present to prevent. 



27139°— 18— Bull. 647 3 



